There is known a hybrid construction machine such as a power shovel with an engine and a motor generator. The hybrid construction machine generates electric power by rotating a generator by means of an excess output of the engine, and/or generates power by rotating the motor generator by means of energy discharged from an actuator. The power generated in this way is used to rotate the motor generator, and a hydraulic motor and the like are driven by means of the rotation of the motor generator.
JP2009-235717A discloses a control device of a hybrid construction machine in which a turning pressure of the turning motor is utilized as regeneration energy. This control device causes a fluid pressure motor to rotate by utilizing pressure of a fluid discharged from a boom cylinder at the time of lowering a boom or the turning pressure of the turning motor, thereby rotating a motor generator to generate electric power or actuating an assist pump coupled to the fluid pressure motor.